The present invention relates generally to mechanical seals for providing fluid sealing between a housing and a rotating shaft. More particularly, the invention relates to a pressure regulation system used to regulate one or more fluids of the mechanical seal.
Conventional mechanical seals are employed in a wide variety of mechanical apparatuses to provide a pressure-tight and fluid-tight seal between a rotating shaft and a stationary housing. The seal is usually positioned about the rotating shaft, which is mounted in and protrudes from the stationary housing. The seal is typically bolted to the housing at the shaft exit, thus preventing loss of pressurized process fluid from the housing. Conventional mechanical seals include face-type mechanical seals, which include a pair of annular sealing rings that are concentrically disposed about the shaft, and axially spaced from each other. The sealing rings each have sealing faces that are biased into physical contact with each other. Typically, one seal ring remains stationary while the other ring contacts the shaft and rotates therewith. The mechanical seal prevents leakage of the pressurized process fluid to the external environment by biasing the seal ring sealing faces into physical contact with each other. As a result of the physical contact between the faces, abrasion of the seal faces occurs and the seals typically exhibit undesirable wear characteristics and leakage. This is particularly related to liquid type seal when operating dry or opened for servicing.
The poor wear characteristics of these conventional mechanical face seals necessitate the frequent monitoring and replacement of the seal components, particularly the seal rings. Replacement and repair of damaged seals have been facilitated by seal designs where a portion of the component parts of the mechanical seals are segmented or split. Installation of split or partially split seal components can be performed without necessitating the complete breakdown of the mechanical apparatus and without having to pass the annular seal over an end of the shaft. However, even in split seal designs, significant time is required to replace the seal components, resulting in frequent long periods of down time for the mechanical apparatus associated with the seal.
The prior art attempted to overcome the above difficulties by employing non-contact mechanical seals that utilize a fluid interposed between the seal ring faces to reduce frictional wear thereof. Conventional mechanical non-contact face seals typically employ spiral-type grooves formed in the face of the rotating seal ring to develop a hydrodynamic lifting force that separates the seal faces. The resultant gap allows fluid to be disposed within the gap to prevent abrasion of the seal faces. These types of seals are limited in application because the seals are designed to operate in a unidirectional manner. If the seals are driven in the opposite direction, the seal rings typically do not separate but are pulled or sucked toward each other, thereby increasing wear and ultimately destroying the seals. Other conventional designs employ specially designed grooves that can operate in both directions called, bi-directional grooves. These grooves, however, typically are expensive to manufacture since they require precise and intricate machining, and are inefficient in providing hydrodynamic lift to adequately separate the seal faces.
Even in mechanical non-contact seal designs a certain amount of seal face abrasion occurs, especially during start-up or during periods in which the shaft is rotating at relatively low speeds. This is due in part to a lack of regulation of the pressures of the various fluids used in the seal. For example, the barrier fluid pressure and the process fluid pressure need to be maintained relative to each other such that the seal faces are not forced apart so far that process fluid may escape, or that the seal faces may be forced into actual physical contact with little or no barrier fluid to protect their surfaces. Such abrasion causing wear of the seal components results in the eventual need to replace the seal components.
As the above described and other prior art seals have proved less than optimal, an object of the invention is to provide a pressure regulation system for regulating the pressures of various fluids within the seal in order to reduce wear, while concomitantly preventing or minimizing leakage at the other faces, without compromising seal performance or integrity, particularly when the various fluid pressures are changing during startup or during low speed operation.
Another object of the invention is to provide a pressure regulation system that is compact and easy to mount relative to the mechanical seal.
Still another object of the invention is to provide a split mechanical seal with a pressure regulation system with sufficient dynamic range so as to be operable under a wide range of operating conditions for a wide range of services.
Yet another object of the invention is to provide a mechanical seal that ensures sufficient hydrodynamic lift adequate for face seal separation during use.
Still yet another object of the invention is to provide a fluid regulation system that regulates the rate of face seal leakage during operation.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the drawings and the description which follow.